LeetCode (F)

First Missing Positive

 

AC Rate: 546/2441

My Submissions

Given an unsorted integer array, find the first missing positive integer.

For example,
Given [1,2,0] return 3,
and [3,4,-1,1] return 2.

Your algorithm should run in O(n) time and uses constant space.

class Solution {public:int firstMissingPositive(int A[], int n) {vector<bool> flag(n + 1, false);for (int i = 0; i < n; ++i)if (A[i] > 0 && A[i] <= n)flag[A[i]] = true;int ans = 1;while (ans <= n) {if (flag[ans] == false) break;++ans;}return ans;}};

Flatten Binary Tree to Linked List

 

AC Rate: 669/2768

My Submissions

Given a binary tree, flatten it to a linked list in-place.

For example,
Given

         1        / \       2   5      / \   \     3   4   6

The flattened tree should look like:

   1    \     2      \       3        \         4          \           5            \             6

click to show hints.

Hints:

If you notice carefully in the flattened tree, each node's right child points to the next node of a pre-order traversal.

class Solution {void inorder(TreeNode *root, vector<int> &vec) {if (root == NULL) return;vec.push_back(root->val);inorder(root->left, vec);inorder(root->right, vec);}public:void flatten(TreeNode *root) {vector<int> vec;inorder(root, vec);if (vec.size() == 0) return;TreeNode *pre = root;for (int i = 1; i < vec.size(); ++i) {TreeNode *tmp = new TreeNode(vec[i]);pre->right = tmp;pre->left = NULL;pre = tmp;}return;}};